Effects of Neostigmine and Pyridostigmine on Duration of Succinylcholine Action and Pseudocholinesterase Activity

Effects of the anticholinesterase drugs on the duration of action of succinylcholine (SCh) and pseudocholinesterase activity were studied in 16 adult patients undergoing general anesthesia. Each patient received two doses of SCh, 1 mg/kg, intravenously: the first dose was given before and the second dose, 5 min after neostigmine, 5 mg, or pyridostigmine, 25 mg. Electromyographic determinations were used to measure the duration of SCh-induced block. Prolongation in the neostigmine group (n = 8) was compared with that in the pyridostigmine group (n = 8). Pseudocholinesterase activities were determined before, during, and at the point of full recovery of neuromuscular blockade by the second dose of SCh.The effect of SCh, 1 mg/kg, was significantly prolonged from the control value, 11.1 ± 1.43 (mean ± SE), to 35 ± 3.24 min following neostigmine, and from 13.1 ± 1.45 to 23.9 ± 2.5 min after pyridostigmine. Pseudocholinesterase activities determined 5 min after administration of neostigmine and pyridostigmine were decreased to 21 and 20 per cent of control, respectively. Full recovery from the SCh-induced block was observed, while enzymatic activities remained suppressed to 47 and 39 per cent of control in the neostigmine and pyridostigmine groups, respectively. The neuromuscular blocking effect of SCh was significantly prolonged by both neostigmine and pyridostigmine, but more by neostigmine. It is concluded that the enzyme may not be the sole factor determining the effect of anticholinesterase drugs on the duration of action of SCh.